Traditional and CPT-based foundation designs: A comparative study

This paper compares traditional foundation design to direct cone penetration testing (CPT) design using CPT data (i.e., measured cone tip resistance, sleeve friction, and/or measured porewater pressure). Shallow foundations have traditionally been designed in a two-part process to approximate the required size and shape of a foundation: determining the bearing capacity and expected settlement (commonly referred to as displacement) of the soil. The Minnesota Department of Transportation (MnDOT) has created an easy to follow CPT design manual, establishing a process for shallow foundation design directly using CPT data. A systematic procedure is available to transition from the CPT data to bearing capacity accounting for settlement. This paper will focus on applying the design guide to an existing project in Minnesota. The paper will describe a case history from a bridge replacement on TH 24 over the Mississippi River in Clearwater, Minnesota. This project used traditional methods for shallow foundation design and is reexamined using the new MnDOT CPT guide. This study demonstrates efficiency of using direct CPT design in geotechnical practice.